The present invention relates to the radiographic arts. It finds particular application in conjunction with x-ray tubes for computerized tomographic (CT) scanners and will be described with particular reference thereto. However, it is to be appreciated that the present invention may also be amenable to x-ray tubes for other applications.
CT scanners have commonly included a floor-mounted frame assembly which remains stationary during a scan. An x-ray tube is mounted to a rotatable frame assembly which rotates around a patient receiving examination region during the scan. Radiation from the x-ray tube traverses the patient receiving region and impinges upon an array of radiation detectors. Using the position of the x-ray tube during each sampling, a tomographic image of one or more slices through the patient is reconstructed.
The x-ray tube assembly typically comprises a lead lined housing containing a vacuum envelope or x-ray insert which holds a rotating anode and a stationary cathode. Cooling oil is flowed between the x-ray insert and the housing. In large, high performance x-ray tubes, the x-ray insert may be a metal shell or frame with a beryllium window mounted or brazed thereon for allowing the transmission of x-rays from the x-ray insert. Likewise, the housing defines an x-ray output window that is in alignment with the beryllium window of the x-ray insert such that x-rays may pass directly through the beryllium window and the x-ray output window.
During x-ray generation, electrons are emitted from a heated filament in the cathode and accelerated to a focal spot area on the anode. Upon striking the anode, some portion of the electrons, or secondary electrons, are bounced to the surrounding frame and converted into heat. The beryllium window receives the highest intensity of the secondary electron heating because the window is closer to the focal spot on the anode. The heat is undesirable and is commonly termed waste heat. One of the persistent problems in CT scanners and other radiographic apparatus is dissipating the waste heat created while generating x-rays.
In order to remove the waste heat, a cooling oil is often circulated through the housing and around the x-ray insert forming a cooling jacket around the x-ray insert. For example, oil may be drawn through an output aperture located at one end of the housing, circulated through a radiator or heat exchanger and returned to an inlet aperture in the opposite end of the housing. The returned cooled fluid flows axially through the housing toward the outlet aperture, absorbing heat from the x-ray insert.
Removing waste heat in this manner is not always completely effective. More specifically, waste heat removal by merely forcing coolant to flow between the x-ray insert and the housing is particularly ineffective around the x-ray output window. The beryllium window and its environs, being the recipient of the secondary electrons and heat from the closely adjacent focal spot, is preferentially heated. Further, the beryllium window protrudes out from the frame and generally disrupts the flow of coolant around the window preventing optimal cooling. Additionally, the configuration of the x-ray output window on the housing disrupts coolant flow and, by its proximity to the beryllium window, limits the amount of coolant capable of passing over the beryllium window.
When the window is not sufficiently cooled, the heat can damage the braze joint between the beryllium window and the x-ray insert causing the x-ray tube to fail. Further, the coolant adjacent to the beryllium window may boil and leave a carbon residue on the beryllium window. Such a coating is undesirable as it may degrade the quality of the x-ray image.
The present invention provides a new and improved cooling system and technique for overcoming the above-reference drawbacks and others.
The present invention relates to the use of a cold-plate on the x-ray window of an x-ray insert to provide for the removal of undesirable waste heat from an x-ray tube.
In accordance with one aspect of the present invention, a CT scanner comprises an x-ray tube assembly mounted on a rotating frame portion. The x-ray tube assembly includes a housing, an x-ray tube operatively mounted within the housing, and a cooling fluid reservoir defined between the x-ray tube and the housing. The cooling fluid reservoir includes an inlet aperture through the housing and an outlet aperture through the housing. The CT scanner also comprises an x-ray window mounted on the x-ray tube, a cooling fluid circulation line, and a cooling fluid return line. The circulation line is in fluid communication with the inlet aperture of the cooling fluid reservoir and with a heat exchanger. The return line is in fluid communication with the heat exchanger and the outlet aperture of the cooling fluid reservoir. The CT scanner additionally comprises a pump and a cold-plate mounted on the x-ray tube around the x-ray window. The pump circulates the cooling fluid through the heat exchanger, the suction and return lines, and the x-ray tube housing assembly.
In accordance with another aspect of the present invention, an x-ray tube assembly comprises a housing, an x-ray tube, and a cold-plate. The housing has an x-ray window and defines a housing cavity therein. The x-ray tube includes a vacuum envelope which holds an anode and a cathode. The vacuum envelope has an x-ray translucent window adjacent the anode. The x-ray tube is mounted in the housing cavity spaced from the housing to define a cooling fluid reservoir therebetween and the x-ray translucent window is aligned with the x-ray window. The cold-plate is operatively mounted on the x-ray translucent window.
In accordance with another aspect of the present invention, an x-ray tube comprises a cold plate and a vacuum envelope having an anode and a cathode with an x-ray window mounted thereon adjacent the anode. The cold plate includes an elongated shell and a plurality of heat transfer elements positioned therein. The shell is operatively mounted around the x-ray window and circumferentially oriented relative to the vacuum envelope. The shell includes an inlet defined in a first end, an outlet defined in an opposite end, and an expansion section disposed therebetween.
In accordance with another aspect of the present invention, a method of cooling an x-ray tube is provided. A first portion of a cooling fluid is circulated over an x-ray tube to remove heat. A second portion of the cooling fluid forced around an x-ray translucent window disposed on the x-ray tube removes heat from the window. The cooling fluid is cooled and recirculated around the window and over the x-ray tube.
The advantages of the present invention include the ability to prevent or reduce the risk of thermal damage to the joint between the beryllium window and the x-ray insert.
Another advantage resides in reducing or preventing failure of the x-ray tube due to overheating.
Another advantage of the present invention resides in reducing or preventing carbon build-up on the beryllium window due to overheating of the cooling fluid.
Another advantage of the present invention resides in maintaining the dielectric characteristics of the cooling fluid to decrease the possibilities of high-voltage instabilities.
Still other advantages and benefits of the invention will become apparent to those skilled in the art upon a reading and understanding of the following detailed description.